The present invention relates to a stacked piezoelectric ceramics displacement magnifying device (which will be hereinafter also referred to as a piezoelectric actuator).
The stacked piezoelectric cermics is constituted of a plurality of stacked ceramics elements displaceable upon application of an electric field thereto. The amount of displacement (distorsion) of the stacked ceramics elements varies with the strength of electric field. As the product of the displacement and a force generated is relatively large, and responsiveness is remarkably high, the stacked piezoelectric ceramics is used as a high-responsive actuator in various fields.
However, the amount of displacement of the stacked piezoelectric ceramics is small, and therefore, an actuator having the stacked piezoelectric ceramics combined with a displacement manifying device is being developed. Such a piezoelectric actuator is disclosed in Japanese Patent Laid-Open Publication No. 60-81568, for example.
Referring to FIG. 3 which shows the conventional piezoelectric actuator, a flexing member 1 is formed of an elongated elastic material which is easily flexible in a horizontal direction shown, but is hardly expandable in a vertical direction shown. The flexing member 1 is connected at its both ends to upper end portions 2c of a lever arm 2 under a preliminarily flexed condition as shown. Lower end portions 2b of the lever arm 2 is connected through hinges 3 to fulcrum portions 4a of a base member 4. The hinges 3 are formed of a sheet material which is hardly expandable in a longitudinal direction thereof. In this example, the hinges 3 are formed integrally with the lever arm 2 and the base member 4. A stacked piezoelectric ceramics 5 is fixed at its upper end to the base member 4, and is connected at its lower end through hinges 6 to lower end portions 2a of the lever arm 2. The hinges 6 are formed of a sheet material similar to the hinges 3. Upon application of a voltage to the stacked piezoelectric ceramics 5, the lower ends of the ceramics 5 are displaced downwardly to rotate the lever arm 2 about the hinges 3. Accordingly, the upper end portions 2c of the lever arm 2 are displaced in the longitudinal direction of the flexing member 1 to deform the flexed central portion of the flexing member 1 into a straight condition. Thus, the amount of displacement of the stacked piezoelectric ceramics 5 may be magnified.
In operation, forces are applied to the lower end portions 2a and the upper end portions 2c of the lever arm 2 as depicted by vectors A' and C'. The product of the vectors A' and C' is shown by a vector B' in FIG. 4, which is applied to the fulcrum portions 2b. However, the longitudinal direction of the hinges 3 connected to the fulcrum portions 2b is not parallel to the direction of the vector B', and accordingly, a bending force as well as a tensile force is applied to the hinges 3. That is, upon application of an electric field to the piezoelectric ceramics 5, the hinges 3 are bent so that the displacement of the piezoelectric ceramics 5 cannot be sufficiently magnified.